1. Field of the Invention
The invention relates to an apparatus of high dynamic-range CMOS image sensor and method thereof, and more particularly, to an apparatus of high dynamic-range CMOS image sensor and method thereof that providing charge supplement to the photodiode.
2. Description of the Prior Art
Dynamic range is an important norm to evaluate quality of an image sensor. Larger the dynamic range, larger the sensible range from lowest sensible signal to highest unsaturated signal of the image sensor is.
Technologies of designing image sensors with high dynamic ranges can be classified into various methods: photonic signal compression, multiple sampling, exposure-time adjustment and so on. In the conventional technologies, the photonic signal compression method will lower the sensitivity of an image sensor, especially the signal noise ratio will be smaller under low illumination, and the Correlated Double Sampling (CDS) circuit cannot be used to reduce the Fixed Pattern Noise (FPN) due to no reset signal, so the image quality is limited. In addition, this method combining linear and logarithmic integration modules will make extra power consumption and increase design complexity of the signal processing circuit. The methods of multiple sampling and exposure-time adjustment can achieve high sensitivity and increase the dynamic range, but the exposure time must be adequately controlled by the complex backend circuit. This backend circuit will enlarge the chip size, and its processing time will reduce the reading speed that makes the sensor cannot capture images immediately.
Hence, the present invention discloses an apparatus of high dynamic-range CMOS image sensor and method thereof to overcome the above-mentioned drawbacks.